Cluster-II Science Operations


JSOC's prime task is to support the coordination of Cluster-II payload science operations by ESA's Cluster Project Scientist. This coordination is particularly demanding for Cluster.
  • It is a PI-class mission, so the principal investigators for the eleven instruments will retain a major role in instrument control throughout the mission. (Note that this is very different from an observatory-class mission, such as XMM, for which the major role in instrument control is delegated to a single centre.)
  • The instruments on Cluster-II will measure many different properties of the natural plasma environment in near-Earth space (magnetic and electric fields, ions and electrons, waves). To maximise the scientific return from the mission, the modes of the individual instruments must be coordinated - to ensure that the different measurements are complementary.
  • To assist the coordination of the scientific measurements made by the different instruments, the Cluster-II instruments can exchange data via an on-board inter-experiment link (IEL). Thus the instrument modes must be coordinated to ensure that an instrument receiving data via the IEL is in a mode consistent with the mode of the instrument sending the data.
  • Instrument operations on the four spacecraft must also be coordinated to ensure that data from the four spacecraft can be compared to derive the spatial and temporal changes that are a prime science objective of the Cluster-II mission.
  • JSOC will carry out this coordination under the direction of the Cluster Project Scientist. It will be the interface through which the Principal Investigators will submit inputs to included in the payload command schedule and will receive feedback on the status of those inputs. To support its work JSOC also has a number of interfaces with the Cluster-II operations control centre at ESOC, which is responsible for overall spacecraft operations. These JSOC interfaces are illustrated in the figure below.
    JSOC interface overview

    Some History

    JSOC was orginally prepared and validated for the Cluster-I mission. The JSOC system was formally initialised ready for science operations on 3 June 1996 and thus was fully operational at the time of the ill-fated launch of Cluster-I on 4 June 1996.

    The JSOC system for Cluster-II is essentially the same system as was developed for Cluster-I. Some changes have been made: (a) to accommodate changes in the overall mission (different ground stations, different phase of the solar cycle), (b) to install upgrades of proprietary software used in the JSOC system (e.g. the Solaris operating system, the Oracle database) and (c) to make a few changes that will improve operational efficiency.

    Pre-launch phase

    The pre-launch phase which commenced in autumn 1998 and runs up to launch. During this phase:

  • the existing Master Science Plan (MSP) for the first and second constellations will be revised and extended as necessary for Cluster-II. (The MSP is the overall science plan that specifies the timeline of data gathering periods on the four spacecraft and the telemetry rates to be used during those periods -a graphical representation of the plan is available as a Bryant plot. Constellations are periods of roughly six months between major manoeuvres which alter the inter-spacecraft separation.)
  • the plan for the inter-experiment interference campaign will be reviewed and completed. This week-long campaign is a vital scientific objective. It will check for interactions between the different instruments and especially for effects of any of the active instruments (ASPOC, EDI, WHISPER) on any other instruments. This is vital to the interpretation of data from the Cluster-II payload.
  • the JSOC command database will be revised to incorporate agreed changes in instrument operation. JSOC has preserved its database from Cluster-I but this must be reviewed by PIs and JSOC to identify the changes needed for Cluster-II (e.g. removal of Cluster-I patches now incorporated in on-board software, etc.)
  • the JSOC-PI interfaces will be re-confirmed as part of ESA's end-to-end test of all Cluster-II systems. This test includes preparation of an instrument command schedule by JSOC, its execution during ground testing of one of the spacecraft, the collection of telemetry during that test and the processing of that telemetry by the Cluster-II ground segment. Thus it will check all interfaces in the Cluster-II systems.
  • a complete command simulation exercise is performed to (re-)train PI, JSOC and ESOC staff in the operation of the commanding system. This exercise will be similar to the commanding system tests carried out for Cluster-I, which proved to be valuable training exercises for all parties. But, for Cluster-II, the primary objective will be training and not testing.
  • various items of PI software will be re-delivered to JSOC and the appropriate acceptance tests will be re-executed. This software will be run by JSOC as part of its monitoring task. It will allow JSOC to monitor the inter-calibration between similar quantities measured on different instruments and different spacecraft - and thus to give early warning of any problems that could affect the quality of Cluster-II data products. This inter-calibration is a major issue for all space plasma missions but is absolutely vital for the comparison of data between the four Cluster-II spacecraft. JSOC will also run some PI software to carry out specific monitoring tasks requested by individual PIs. Re-delivery of the software will allow JSOC and PIs to confirm the version of software used by JSOC.
  • Commissioning Phase

    This phase begins after all four spacecraft reach the operational orbit and runs for about three months. During this phase

  • there will be two JSOC commissioning periods. These are the first periods for which JSOC will assemble a real (but simplified) command schedule. For the first of these periods JSOC will command FGM on a single spacecraft for a few hours and for the second JSOC will command FGM, PEACE, RAPID and WEC (list tbc) on two spacecraft for two (tbc) orbits. These periods will demonstrate payload operation via a JSOC-prepared command schedule and thus act to commission JSOC for full operations.
  • Execution of the inter-experiment interference campaign. This campaign is scheduled to take place at the end of the commissioning phase. It requires the closely coordinated operation of all Cluster-II instruments. JSOC will prepare the command schedule for this period using a detailed plan drawn up in collaboration with a number of campaign coordinators
  • Further inter-experiment interference campaigns are likely to take place during mission operations. JSOC will prepare these by re-using the orginal campaign input as supplemented by additional inputs from the PIs and the campaign coordinators.
  • Mission Operations Phase

    This phase begins immediately after the commissioning phase and is scheduled to continue for at least two years. It is divided into planning periods each of which covers three orbits of the spacecraft (= 3 x 57 = 171 hours, or just over a week).

    During this phase JSOC will generate the payload command schedule for each planning period as shown in the figure below. JSOC will generate a draft command schedule for each instrument (based on the instrument modes specified in the Master Science Plan) and iterate this with the responsible PI. JSOC will then merge the instrument command schedules to produce the payload command schedule and deliver this to ESOC. ESOC will process the payload command schedule and report the results to JSOC. JSOC will assess these results and, if necessary, make any required changes to the command schedules. JSOC commanding scenario

    The first draft of the instrument command schedules will be released to the PIs eight weeks before execution on the spacecraft. The PIs will then revise that draft so that JSOC can merge the instrument command schedules to produce a first draft of the payload command schedule and deliver this to ESOC six weeks before execution on the spacecraft. The PIs can then request JSOC to make further changes in the command schedule (e.g. to take account of problems reported by ESOC). This revision must be complete approximately two weeks before execution on the spacecraft, so that JSOC can deliver the final version of the payload command schedule to ESOC. This final delivery has a deadline at 12:00 UTC on the Tuesday preceding the week (Monday to Sunday) in which the planning period starts. As a result of this system, JSOC will, at any one time, be preparing the payload command schedules for up to eight planning periods. This is illustrated in the figure below. JSOC planning cycle

    JSOC will also generate a number of products to support the planning of Cluster science operations. These include the positions of the four spacecraft - both in geometric terms (GSE x, y and z) and in magnetic terms (magnetic local time, McIlwain L value, magnetic field strength B). They also include the predicted times and locations (GSE x, y and z, magnetic local time, GSM latitude) of various scientific events, e.g. magnetopause and bow shock crossings, neutral sheet crossings, auroral zone and L-shell crossings. The scientific events are predicted for all four spacecraft and for the centroid of the operational spacecraft. These products are made directly available to a number of important users: (i) JSOC is itself a user as the events data are used in its commanding sub-system, (ii) they are disseminated to the Science Working Team via this webserver, and (iii) planning data for co-ordination of Cluster observations with ground-based STP instruments is supplied to the Cluster Ground-based data centre. In addition, selected planning products are also disseminated to the wider Cluster community via the Cluster Data Management System as CDF-formatted files. JSOC planning system

    Last updated by  Mike Hapgood ( M.Hapgood@rl.ac.uk), 18 December 1999


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